ProjectSummary Theobjectiveoftheproposedprojectistoexaminehowvisualandvocalsocialrhythmicentrainmentscaffolds languagedevelopmentintypicallydevelopinginfantsandthoseatriskforautismspectrumdisorder(ASD). ASDisacommonandlifelongneurodevelopmentaldisordercharacterizedbyimpairmentsinsocial communicationandrepetitivebehaviors.Yet,thereisstrikingheterogeneityinlanguageacquisitioninchildren withASD.Additionally,languagedelaysinASDareoftenafirstconcernforparentsthattheirchildisnot developingasexpected.Elucidatingindividualdifferencesinlanguageacquisitionandpromotingmeaningful languagedevelopmentinASDisofutmostimportancebecauselanguageabilitiesarelinkedwithlong-term outcome.Intypicallydevelopinginfants,rhythmplaysacrucialroleinsocialcommunicationandlanguage development.Thisisexemplifiedbycaregivers?useofhighlyrhythmicinfant-directedspeechandsingingto attractandmaintaintheirinfants?attention.Infantsattendtorhythmatmultiplelevelsincludingtheacoustic speechsignal(e.g.,rhythmicstresscues)andthesocialinteractioninwhichspeechisembedded(e.g., rhythmicallycoordinatedeyegaze,gestures,vocalizations).Individualdifferencesinsocialrhythmsensitivity maybeamarkerofsocialattunementandserveasanimportantpredictorofindividualdifferencesinlanguage developmentinASD.ThisR21extendsourpriorworkdemonstratingrhythmicallyentrainedeyegazeintypical infantsandtoddlerstoinfantsat-riskforASDbyexaminingrhythmicsocialvisualengagementusingnovel eye-trackingparadigms(Aim1)andrhythmicsocialvocalengagementbasedonaninnovativemarkerof speechrhythms(Aim2).Moreover,weproposetoexaminewhethervisualandvocalsocialentrainment predictindividualdifferencesinlanguageacquisition(Aim3).ThisresearchiswellalignedwithNIDCD?sfocus onlanguageacquisitioninchildrenwithASD.Thesefindingsareexpectedtoprovidepreliminarydatatoguide futurelongitudinalinvestigationsofsocialentrainmentandlanguagedevelopmentinASD.Thisresearchmay leadtothedevelopmentofbiomarkersofrhythmicentrainmentthatmayinformearlyASDassessmentand diagnosis,aswellasinterventionstrategiesthat,ifwarranted,includerhythmandtimingofsocialinteractions asoneaspectofcomprehensivelanguageinterventionforthesechildren.